1. Field of the Invention
The present invention relates to a single-phase AC synchronized motor, in particular, to a single-phase AC synchronized motor as that the single-phase AC synchronized motor is adapted to shift to synchronized operation by means of a synchronized operation circuit at the point of time that the rotational speed of a permanent magnet rotor does not exceed a synchronized rotational speed at a starting operation.
2. Description of the Related Art
In conventional single-phase AC synchronized motors, Japanese Patent No. 4030571 (hereinafter referred to as the “Patent Document 1”) discloses that a starting operation as a DC brushless motor is performed so as to raise the rotational speed of a rotor up to a synchronized rotation. AC current is then applied to a motor coil for switching over to a synchronized operation as an AC synchronized motor.
The single-phase AC synchronized motor disclosed by the Patent Document 1 comprises: a start-up operation circuit; a synchronized operation circuit that performs a synchronized operation as an AC synchronized motor by applying AC current to a motor coil; an operation selector switch that is provided between a single-phase AC power and the motor coil and that switches over between electric conduction to the start-up operation circuit and electric conduction to the synchronized operation circuit; and a control means that shifts the motor to the synchronized operation by switching over the operation selector switch from the start-up operation circuit to the synchronized operation circuit. Here, in the above start-up operation circuit, AC current supplied from the single-phase AC power is rectified by means of a rectifier bridge circuit; DC current that is smoothed by means of a filter circuit is produced; the direction of motor current is switched over by switching a switching means for start by means of detecting signals from a detecting sensor that detects the position of magnetic poles of a permanent magnet rotor; and a motor coil connected to the single-phase AC power is then electrically conducted. Accordingly, the start-up operation circuit can perform a start-up operation as a DC brushless motor.
Further, while controlling the operation selector switch to be as that the single-phase AC power is connected to the start-up operation circuit, the control means starts the motor through a switching control over a switching means for start according to the detecting signals of the detecting sensor. When the rotational speed of the permanent magnet rotor reaches to a predetermined rotational speed nearby a synchronized rotational speed, a motor current waveform where its phase is more delayed than the output waveform of the detecting sensor is made as that an electrification direction is switched over at least at the zero-cross point of the sensor output waveform. Accordingly, since the motor starts and drives while reducing the electrified range of the motor current, the rotational speed of the rotor can be increased up to the synchronized rotational speed while reducing the occurrence of reverse running torque at the starting operation thereby being stably led to synchronization.
However, the single-phase AC synchronized motor disclosed in the Patent Document 1 has the following problems. First, in the single-phase AC synchronized motor, since start and acceleration are performed by a single-phase full-wave drive through a sensor, a phase becomes detectable after exceeding an AC synchronized rotational speed, subsequently switching over to AC synchronized operation. In this method, there is a case that the switch-over operation becomes unstable depending on motors or the operation environments of the motors. Second, in this single-phase AC synchronized motor, since a rectifier wave is smoothed, it makes necessary to have a large and a high-capacity smoothing capacitor. Because excessive current of more than 5 A is flowed from a bridge diode to the smoothing capacitor, it becomes prerequisite to choose large-sized diodes.